Robert Johansen
@srfbob1.bsky.social
Retired geek (general electronics engineering knowledge), specializing in RF electronics, design and make things, ham radio enthusiast, reader and cat lover.
Remembering my sister, she passed away on this day November 25. 2021
November 25, 2025 at 3:18 PM
Remembering my sister, she passed away on this day November 25. 2021
I have a big Variac, could dim the entire house. I use a small 5A one that I built in to a box with panel meters and isolation transformer and 100W bulb current limiter the most.
November 24, 2025 at 3:05 PM
I have a big Variac, could dim the entire house. I use a small 5A one that I built in to a box with panel meters and isolation transformer and 100W bulb current limiter the most.
Bench test, OK, Frequency adjusted to 1500 KHz, scope shows waveform, half sine wave
November 23, 2025 at 5:11 PM
Bench test, OK, Frequency adjusted to 1500 KHz, scope shows waveform, half sine wave
RCA phono oscillator 1935, it is an accessory that was connected to an AM radio so that a phonograph could be played through the radio. Its a low power transmitter. I built many of these low power transmitting circuits when I was a kid. This is the oldest circuit I have seen. NJARC swap meet find.
November 23, 2025 at 6:08 AM
RCA phono oscillator 1935, it is an accessory that was connected to an AM radio so that a phonograph could be played through the radio. Its a low power transmitter. I built many of these low power transmitting circuits when I was a kid. This is the oldest circuit I have seen. NJARC swap meet find.
Underneath the chassis, D cell for filament circuit, Three 9V batteries for plate circuit. Small white trimpot across "tickler" plate ciruit feedback coil was needed, oscillation was too strong. Regens require just a little oscillation. Phasing also important, needed to reverse the tickler polarity
November 20, 2025 at 8:31 PM
Underneath the chassis, D cell for filament circuit, Three 9V batteries for plate circuit. Small white trimpot across "tickler" plate ciruit feedback coil was needed, oscillation was too strong. Regens require just a little oscillation. Phasing also important, needed to reverse the tickler polarity
Simple one tube regenerative SW receiver. I wound the coil many decades ago, was sitting in a box full of parts. Finally got around to do some metal work building the chassis. Had to make a few circuit modifications to get it to work properly.
November 20, 2025 at 8:19 PM
Simple one tube regenerative SW receiver. I wound the coil many decades ago, was sitting in a box full of parts. Finally got around to do some metal work building the chassis. Had to make a few circuit modifications to get it to work properly.
I was running some speaker impedance measuring tests earlier today in my bedroom. Lucky was my helper, pawing alligator test clips.
November 14, 2025 at 2:55 AM
I was running some speaker impedance measuring tests earlier today in my bedroom. Lucky was my helper, pawing alligator test clips.
I miss my mom, dad, sister every day
November 12, 2025 at 5:54 PM
I miss my mom, dad, sister every day
Remembering my dad on Veterans day. He fought in the Pacific during WWII was a private in U.S Army infantry, hand to hand combat. He suffered with PTSD, was bipolar, could not forgive himself for killing. Rest in peace Dad.
November 11, 2025 at 4:39 PM
Remembering my dad on Veterans day. He fought in the Pacific during WWII was a private in U.S Army infantry, hand to hand combat. He suffered with PTSD, was bipolar, could not forgive himself for killing. Rest in peace Dad.
Lucky says trick or treat
October 31, 2025 at 10:44 PM
Lucky says trick or treat
Bad selenium rectifier
October 27, 2025 at 2:23 PM
Bad selenium rectifier
Hallicrafters S-72 portable AM-SW chassis that I am slowly restoring.
Replaced line cord and selenium rectifier, Selenium rectifiers get weak with age, this one had a large voltage drop. Radio came to life after replacing with a silicon diode, mounted on a terminal strip bottom right of picture.
Replaced line cord and selenium rectifier, Selenium rectifiers get weak with age, this one had a large voltage drop. Radio came to life after replacing with a silicon diode, mounted on a terminal strip bottom right of picture.
October 27, 2025 at 2:21 PM
Hallicrafters S-72 portable AM-SW chassis that I am slowly restoring.
Replaced line cord and selenium rectifier, Selenium rectifiers get weak with age, this one had a large voltage drop. Radio came to life after replacing with a silicon diode, mounted on a terminal strip bottom right of picture.
Replaced line cord and selenium rectifier, Selenium rectifiers get weak with age, this one had a large voltage drop. Radio came to life after replacing with a silicon diode, mounted on a terminal strip bottom right of picture.
At NJARC repair clinic earlier today
October 25, 2025 at 8:58 PM
At NJARC repair clinic earlier today
Any guesses what this is ?
I picked it up at the VCF East swap meet yesterday
Bench test, after a little coaxing it works.
I picked it up at the VCF East swap meet yesterday
Bench test, after a little coaxing it works.
October 19, 2025 at 8:34 PM
Any guesses what this is ?
I picked it up at the VCF East swap meet yesterday
Bench test, after a little coaxing it works.
I picked it up at the VCF East swap meet yesterday
Bench test, after a little coaxing it works.
Calibrating (de-embedding) my new Digital wattmeter using a HP437B power meter with attenuator and thermistor mount.
October 13, 2025 at 1:56 PM
Calibrating (de-embedding) my new Digital wattmeter using a HP437B power meter with attenuator and thermistor mount.
Crosley pup 1920's regen radio with repro A cell and B battery in my collection
October 8, 2025 at 12:59 PM
Crosley pup 1920's regen radio with repro A cell and B battery in my collection
Nice, animals are wonderful. I have one house cat and feed some feral's. I lost my cat Pawlette she was 18 in February. I took in a stray cat. Named it Lucky.
October 7, 2025 at 11:56 PM
Nice, animals are wonderful. I have one house cat and feed some feral's. I lost my cat Pawlette she was 18 in February. I took in a stray cat. Named it Lucky.
1296 MHz amplifier control box, EME
WWII radio destruct switch
AMSAT cubesat simulator
WWII radio destruct switch
AMSAT cubesat simulator
October 6, 2025 at 2:54 PM
1296 MHz amplifier control box, EME
WWII radio destruct switch
AMSAT cubesat simulator
WWII radio destruct switch
AMSAT cubesat simulator
Ping pong anyone ?
October 5, 2025 at 1:52 PM
Ping pong anyone ?